Doubt it will be anything else than what you describe bud.
Any reel error (Reel 1 in this case), would normally relate to an issue with the opto on said reel, so what I would do here, is swap reel 1 wiring connector with reel 2, and see if the fault transfers itself to reel 2...... if it does (Should be error 2.2 / reel 2, if memory serves me right), then fault is somewhere on that reel, but if not, then it will be elsewhere, like possibaly on the MPU end.
If you have traced the fault to reel 1, then yes I would first clean the opto, and also check that the opto flag on the reel is in it's correct place, by looking at the other reels and see how they are set up, also making sure that a small LED comes on when the machine is powered up (Even if only briefly).
If this don't work, then I would advise swapping an opto sensor from another reel (The 1 - 12 game reel would be best), and see if the fault moves again like you did with the reel wire swap earlier.